Method for determining the horizontal airspeed of helicopters in low speed ranges

Abstract

A method is disclosed for determining the horizontal airspeed of helicopters in low speed ranges. At least three control functions, θ o ,i (collective pitch), θ s ,i (longitudinal control) and θ c ,i (lateral control) are measured. The magnitude of the horizontal airspeed, V H ,i, is determined from its known relationship to θ o ,i. This magnitude is included in non-linear calibration equations θ s (V H , ψ) and θ c (V H , ψ) and control profiles θ s (V H ,i, ψ) and θ c (V H ,i, ψ) are derived therefrom. The measured values θ s ,i and θ c ,i are applied to the respective control profiles and corresponding phase pairs ψ s ,1, ψ s ,2 and ψ c ,1, and ψ c ,2 located. The pairs are compared and the incident flow angle ψ i is determined as the value common to the two pairs. From this information, the components of the horizontal airspeed are found from the relationships: V.sub.x,i =V.sub.H,i Cos ψ.sub.i V.sub.y,i =V.sub.H,i sin ψ.sub.i.

What is claimed is: 
     
       1. A method for determining the horizontal airspeed of a helicopter in low speed ranges comprising the steps of: (a) determining a first relationship between collective pitch θ o  and airspeed V H  for said helicopter; and   (b) determining a second relationship for said helicopter between longitudinal control value θ s  and air-speed V H  for a plurality of directions of incident air flow ψ; and   (c) determining a third relationship for said helicopter between lateral control value θ c  and airspeed V H  for a plurality of directions of incident air flow ψ; then   (d) storing said first, second and third relationships; then   (e) detecting values θ o ,i, θ c ,i and θ s ,i ; then   (f) determining horizontal airspeed magnitude V H ,i from said first stored relationship and θ o ,i ; then   (g) deriving a longitudinal control profile θ s  (V H ,i, ψ) from said airspeed magnitude and the values of said second stored relationship; and   (h) deriving a lateral control profile θ c  (V H ,i, ψ) from said airspeed magnitude and the values of said third stored relationship; then   (i) applying the detected value of lateral control θ c ,i to said lateral control profile to determine a corresponding first pair of incdient angles ψ c ,1 and ψ c ,2 ; and   (j) applying the detected value of longitudinal control θ s ,i to said longitudinal control profile to determine a corresponding second pair of incident angles ψ s ,1 and ψ s ,2 ; then   (k) comparing said first and second pairs of incident angles;   (l) selecting a value common to said incident angle pairs as the incident angle value ψ i  ; and then   (m) calculating the components of horizontal airspeed as:   V.sub.x,i =V.sub.H,i cos ψ.sub.i       V.sub.y,i =V.sub.H,i sin ψ.sub.i.       
     
     
       2. A method as defined in claim 1 wherein the values of the control angles θ o , θ c  and θ s  are measured as helicopter control functions. 
     
     
       3. A method as defined in claim 2 wherein the measured control functions values are supplied directly by signal generators connected to helicopter control levers. 
     
     
       4. A method as defined in claim 2 wherein the measured control functions values are supplied by synchros connected to helicopter control levers. 
     
     
       5. A method as defined in claim 2 wherein the measured control functions values are supplied by resolvers connected to helicopter control levers. 
     
     
       6. A method as defined in claim 1 wherein said first, second and third relationships are determined by means of calibration test flights.